1. Field of the Invention
The present invention relates to a color conversion definition creating apparatus for creating a color conversion definition defining a coordinate conversion in a mutual relationship between two color spaces.
2. Description of the Related Art
Hitherto, when a color-printing machine is used to perform a color image printing, it is performed prior to the color image printing that a color printer and the like is used to create a proof image which is extremely similar in color to an image to be printed in the color-printing machine. When the color printer and the like is used to create the proof image, there is derived a printing profile (a color conversion definition) describing a relation between image data and colors of actual printed matters, associated with using conditions, such as a type of a printing machine of interest, sorts of ink to be used in the printing machine, and sheet quality of sheets to be subjected to printing, which will be referred to as printing conditions. Further, there is also derived a printer profile (a color conversion definition) describing a relation between image data and colors of images actually printed out, associated with using conditions, such as a type of a printer, using conditions of the printer, which will be referred to as print conditions. The image data for printing is converted into the image data for a printer in accordance with a combined color conversion definition wherein the printing profile is combined with the printer profile, so that a proof image is created in accordance with the image data for a printer thus converted. In this manner, it is possible to create the proof image, which is coincident with the actual printed matter in color to some extent.
By the way, any colors of the color printed matter can be implemented in principle by a combination of three colors of C (cyan), M (magenta), and Y (yellow). However, inks associated with those three colors do not always have ideal spectral characteristics. For this reason, in the usual printing, a color printed matter is created with four colors including K (black). Therefore, in order to create a proof image with greater accuracy, it often happens that CMYK four colors are used also in a printer for crating a proof image.
Thus, in the event that an image of the printed matter and the proof image are created with CMYK four colors, the printing profile and the printer profile define a conversion relation between four-dimensional data of CMYK and three-dimensional data of calorimetric values, such as L*a*b* (hereinafter, it is simply denoted in form of Lab). The combined color conversion definition defines four-dimensional data of CMYK for printing and four-dimensional data of CMYK for a printer.
In the event that the combined color conversion definition is created, four-dimensional data of CMYK for printing and four-dimensional data of CMYK for a printer are associated with one another via three-dimensional data of calorimetric values. Since a degree of freedom in four-dimensional data of CMYK is higher than that of three-dimensional data of calorimetric values, it is impossible to determine uniquely the combined color conversion definition unless some restriction is applied to four-dimensional data of CMYK. In view of the foregoing, according to the prior art, there is proposed such a restriction that a K-component in four-dimensional data of CMYK is saved.
A restriction of saving the K-component is effective in the event that a density of ink of K-color in a printing machine is close to a density of ink of K-color in a printer. However, in the event that those densities are greatly different from each other, a printed matter by a proof image is low in accuracy of reproduction of color, and thus it would cause such a problem that an atmosphere in looking at the proof image is different from an atmosphere of the printed matter. In addition, as color reproduction ability in a printer, although there is left scope to bring a color of the proof image close to a color of the printed matter, it is difficult to make good use of the color reproduction ability.
On the other hand, in the event that good use of the color reproduction ability is regarded as important and the K-component is established without any restriction, it requires a great deal of time and labor to determine a suitable association. This would make it difficult to create the combined color conversion definition.
Here, while the explanation is made referring to a printing machine and a printer by way of example, the above-mentioned problems are raised in general when the combined color conversion definition defining the conversion relation between the four-dimensional data for CMYK is created via the three-dimensional color space.